In the transfer of bulk particulate material from a vessel to a pneumatic conveying line, rotary valves commonly are used for feeding such material from the vessel to the conveying line. Often, the vessel is at atmospheric pressure so that material in the vessel is gravity fed through the valve to the conveying line in which air under pressure in the range of up to 60 psi is injected to convey material along the line. In some applications, depending on the nature of the material being handled, the vessel also may be pressurized. Under either of such circumstances, a pressure differential is provided across the valve.
Typically, rotary valves of the type described, generally includes a housing defining a cylindrical chamber having an inlet and an outlet, a shaft journaled in the housing, coaxially with the axis of the chamber, and a rotor mounted on the shaft within the chamber, having a plurality of circumferentially spaced pockets which function to receive material through the inlet of the valve and discharge such material through the outlet thereof as the rotor shaft is rotated. The positioning and rotation of the rotor of such valve function not only to pass material through the valve but to maintain the pressure differential across the valve. As pockets of the rotor of such valves communicate with the outlets thereof, discharging material therethrough, they become pressurized. In order for such valves to function properly to feed material therethrough, the pressures in such pockets must be relieved before they again communicate with the inlets of the valves. Such pressure relief commonly is accomplished by providing another outlet in the housing between the material discharge outlet and the material inlet for venting the pressurized air in such pockets to the atmosphere.
As pressurized air is vented from such valves, a high pitched, unpleasant sound is created which is highly objectionable and thus desirable to reduce if not eliminate. Accordingly, it is the principal object of the present invention to provide a high pressure rotary valve of the type described used for feeding bulk particulate materials from a comparatively low pressure zone to a high pressure zone, venting such valves and minimizing if not eliminating the objectionable sound created by the venting of high pressure air.